Registers variable lookup function $prefix. The registered function is executed by the XPath engine each time an XPath variable is evaluated. It takes three arguments: $data, variable name, and variable ns-URI and must return one value: a number or string or any XML::LibXML:: object that can be a result of findnodes: Boolean, Literal, Number, Node (e.g. Document, Element, etc.), or NodeList. For convenience, simple (non-blessed) array references containing only XML::LibXML::Node objects can be used instead of an XML::LibXML::NodeList.

Registers an extension function $name in $uri namespace. $callback must be a CODE reference. The arguments of the callback function are either simple scalars or XML::LibXML::* objects depending on the XPath argument types. The function is responsible for checking the argument number and types. Result of the callback code must be a single value of the following types: a simple scalar (number, string) or an arbitrary XML::LibXML::* object that can be a result of findnodes: Boolean, Literal, Number, Node (e.g. Document, Element, etc.), or NodeList. For convenience, simple (non-blessed) array references containing only XML::LibXML::Node objects can be used instead of a XML::LibXML::NodeList.

Performs the xpath statement on the current node and returns the result as an array. In scalar context, returns an XML::LibXML::NodeList object. Optionally, a node may be passed as a second argument to set the context node for the query.

Performs the xpath expression using the current node as the context of the expression, and returns the result depending on what type of result the XPath expression had. For example, the XPath 1 * 3 + 52 results in an XML::LibXML::Number object being returned. Other expressions might return a XML::LibXML::Boolean object, or a XML::LibXML::Literal object (a string). Each of those objects uses Perl's overload feature to ``do the right thing'' in different contexts. Optionally, a node may be passed as a second argument to set the context node for the query.

That is, it returns the literal value of the results. This enables you to ensure that you get a string back from your search, allowing certain shortcuts. This could be used as the equivalent of <xsl:value-of select=``some_xpath''/>. Optionally, a node may be passed in the second argument to set the context node for the query.

This method behaves like findnodes, except that it only returns a boolean value (1 if the expression matches a node, 0 otherwise) and may be faster than findnodes, because the XPath evaluation may stop early on the first match (this is true for libxml2 >= 2.6.27).

For XPath expressions that do not return node-set, the method returns true if the returned value is a non-zero number or a non-empty string.

Set the current context position. By default, this value is -1 (and evaluating XPath function position() in the initial context raises an XPath error), but can be set to any value up to context size. This usually only serves to cheat the XPath engine to return given position when position() XPath function is called. Setting this value to -1 restores the default behavior.

Set the current context size. By default, this value is -1 (and evaluating XPath function last() in the initial context raises an XPath error), but can be set to any non-negative value. This usually only serves to cheat the XPath engine to return the given value when last() XPath function is called. If context size is set to 0, position is automatically also set to 0. If context size is positive, position is automatically set to 1. Setting context size to -1 restores the default behavior.

XML::LibXML::XPathContext objects are reentrant, meaning that you can call methods of an XML::LibXML::XPathContext even from XPath extension functions registered with the same object or from a variable lookup function. On the other hand, you should rather avoid registering new extension functions, namespaces and a variable lookup function from within extension functions and a variable lookup function, unless you want to experience untested behavior.